Plasma injection modules

ABSTRACT

A plasma injection module includes a fuel receiving end, a discharge end opposite the fuel receiving end, and an axial fluid pathway extending between the fuel receiving end and the discharge end. An insulator assembly defines a first portion of the axial fluid pathway proximate to the fuel receiving end. An injection tube assembly having a permanent magnet is positioned downstream of the insulator. A voltage input connection is arranged downstream of the insulator assembly and upstream of the injection tube assembly. The voltage input connection secures a voltage source to the injection tube to form a plasma filament within and adjacent to the axial fluid pathway. During operation a permanent magnet produces a magnetic field that interacts with the plasma filament to rotate the plasma filament and increase an area of ignition between the plasma filament and the combustible material at the discharge end.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 17/172,311, filed on Feb. 10, 2021, which is related to andclaims the priority benefit of U.S. Provisional Patent Application No.62/975,134, filed on Feb. 11, 2020, the entire contents of each of whichare fully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to advanced fuel injection systems. Inparticular, the disclosure relates to fuel injection systems forsynergistic fuel injection, ignition, and flame maintenance.

INTRODUCTION

Ignition is defined as the transformation process of a combustiblematerial from an unreactive state to a self-propagating state. Ignitioncan be summarized in three successive stages: (1) the igniter (spark inconventional systems) creates initial conditions for chemical energyrelease. The initial break-down phase results in a microsecond scaleelectrically conducting channel, followed by a glow discharge phasewhich deposits most of the energy. The after-spark zone of gas is fullyor partially ionized and contains a pool of highly reactive chemicalspecies. (2) Then the flame develops depending on the initiation of thechemical reactions, which determines whether or not the transition froma kernel of hot gas to a self-sustained flame kernel is possible. (3)The final step of ignition is flame kernel propagation, which leads toflame growth and wrinkling.

A basic fuel injection/ignition system for high-speed combustors isillustrated in FIGS. 1 a and 1 b . The fuel injection/ignition systemtypically includes a flame holding structure having a fuel port thatreceives a combustible material, an ignition source, and a recessedcavity for mixing the combustible material with oxidizer at presence ofthe ignition source to allow the combustible material to ignite (FIG. 1b ).

The use of plasma for fuel ignition and flame holding (in a high-speedenvironment) has seen increased interest because of plasma's potentialto enhance operational stability, make ignition a more reliable process,and reduce total pressure losses under certain flow conditions withoutthe need for mechanical flame holding structures. Plasma-based methodsoffer great advantages in fuel ignition time and flame stability overconventional methods, such as a pilot flame in a cavity or conventionalspark plug ignition.

FIG. 2 illustrates a typical flow structure at fuel injection intosupersonic crossflow. In the illustrated embodiment, the fuel injectionsystem 10, includes a combustor that has a metal wall 14 having a fuelinjection port 18. Many fuel injection systems, used in supersoniccombustors, commonly utilize a subsonic recirculation region known as aflameholder, typically a rear-facing cavity or a wall-step. This is toovercome the orders of magnitude difference in flame propagation speed(order 1 m/s) and flow velocity (order 500 m/s and greater depending onflight Mach number). As the fuel jet interacts with a supersoniccrossflow 26, a bow shock 34 is formed which causes an upstream boundaryor mixing layer 38 to separate. As such, the mixing layer 38 isformed—which is the area for the fuel and the oxidizer to mix downstreamof the fuel outlet 18 at a subsonic velocity. Additionally, in case ofhigh temperature core flow, the bow shock 34 forms autoignition zoneswith an increased heat release rate. If the heat release rate is toohigh, dynamic instabilities or choking may occur. Therefore, the fuelinjection system illustrated in FIG. 2 , uses the supersonic airflow 26to ignite the combustible material. To increase the mixing, the designtypically includes fuel injection struts (not shown). The struts'interaction with supersonic airflow leads to a complex 3D shock wavestructure, which impacts the pressure losses, which is increasinglyevident at higher velocities.

With reference to FIGS. 3 a and FIG. 3 b , a fuel injection system 40that uses a plane wall 44 (e.g., no cavity flame holder) is illustrated.The fuel injection system 40 includes a fuel port 48 in the plane wall44 and a high voltage electrode array 52 is positioned proximate thefuel port 48 on the wall 44. The high voltage electrode array 52generates plasma filaments 54 that interact with a fuel jet entering asupersonic crossflow 26 through the fuel port 48.

The high voltage electrodes 52 may be positioned in front of (upstream,as shown in FIG. 3 a ) or behind (downstream, as shown in FIG. 3 b ) thefuel port 48 with respect to the supersonic crossflow 26. As such, thereis limited control for the fuel-oxidizer interaction, mixing, andignition. This may cause lags in ignition of the fuel and/or inefficientmixing of the fuel and oxidizer.

SUMMARY

In one aspect, a plasma injection module comprises a fuel receiving endconfigured to receive a combustible material, a discharge end oppositethe fuel receiving end, an axial fluid pathway extending between thefuel receiving end and the discharge end, an insulator assembly defininga first portion of the axial fluid pathway proximate to the fuelreceiving end, and an injection tube assembly positioned downstream ofthe insulator assembly. The injection tube assembly coupled to theinsulator assembly, the injection tube assembly including an injectiontube defining a second portion of the axial fluid pathway adjacent tothe discharge end, the injection tube formed of an electricallyconductive material and a nozzle surrounding the injection tube, thenozzle defining a fuel discharge opening proximate the discharge end. Avoltage input connection arranged between the insulator assembly and theinjection tube assembly, the voltage input connection being configuredto secure a voltage source to the injection tube to form a plasmafilament within and adjacent to the axial fluid pathway and a flowinducing device coupled to the injection tube proximate to the dischargeend.

In another aspect, a plasma injection module comprises a fuel receivingend configured to receive a combustible material, a discharge endopposite the fuel receiving end, an axial fluid pathway extendingbetween the fuel receiving end and the discharge end, an insulatorassembly defining a first portion of the axial fluid pathway proximateto the fuel receiving end, a connection assembly positioned downstreamof the insulator assembly and defines a second portion of the axialfluid pathway, and an injection tube assembly positioned downstream ofthe insulator and connection assembly. The injection tube assemblycoupled to the insulator assembly via the connection assembly, theinjection tube assembly including an injection tube defining a thirdportion of the axial fluid pathway adjacent to the discharge end, theinjection tube formed of an electrically conductive material, apermanent magnet arranged annularly about the injection tube proximateto the discharge end, and a nozzle surrounding the injection tube andthe permanent magnet, the nozzle defining a fuel discharge openingproximate the discharge end. A voltage input connection arrangeddownstream of the insulator assembly and the connection assembly andupstream of the injection tube assembly, the voltage input connectionbeing configured to secure a voltage source to the injection tube toform a plasma filament within and adjacent to the axial fluid pathway.

In another aspect, an ignition system comprises a combustor having oneor more fuel ports positioned on a flowside wall, and a plasma injectionmodule coupled to the combustor. The plasma injection module comprisinga fuel receiving end configured to receive a combustible material, adischarge end opposite the fuel receiving end, the discharge end beingpositioned proximate the flowside wall, an axial fluid pathway extendingbetween the fuel receiving end and the discharge end, an insulatorassembly defining a first portion of the axial fluid pathway proximateto the fuel receiving end, and an injection tube assembly positioneddownstream of the insulator assembly. The injection tube assemblycoupled to the insulator assembly, the injection tube assembly includingan injection tube defining a second portion of the axial fluid pathwayadjacent to the discharge end, the injection tube formed of anelectrically conductive material and a nozzle surrounding the injectiontube, the nozzle defining a fuel discharge opening proximate thedischarge end. A voltage input connection arranged between the insulatorassembly and the injection tube assembly and a flow inducing devicecoupled to the injection tube proximate to the discharge end.

Other aspects of the disclosure will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a simple schematic view of a fuel injection/ignition systemaccording to the prior art.

FIG. 1 b is a simple schematic view of the fuel injection/ignitionsystem of FIG. 1 a during ignition.

FIG. 2 is a schematic view that illustrates a typical flow structure atfuel injection into supersonic crossflow.

FIG. 3 a is a schematic view of a previously studied plasma ignitionpattern: a high voltage electrode positioned upstream of a fuelinjection port.

FIG. 3 b is a schematic view of a previously studied plasma ignitionpattern: a high voltage electrode positioned downstream of a fuelinjection port.

FIG. 4 is a perspective view of an exemplary plasma injection moduleaccording to the present disclosure.

FIG. 5 is a side, cross-sectional view of the plasma injection moduleshown in FIG. 4 .

FIG. 6 is a side exploded view of the plasma injection module shown inFIG. 4 .

FIG. 7 is a perspective outside view of an example plasma injectionmodule, coupled to test section insert for SBR-50 at the University ofNotre Dame which emulates a supersonic combustor, according to anembodiment of the present disclosure.

FIG. 8 is a perspective flowside view of the assembly shown in FIG. 7 .

FIG. 9 is a flowside photographic image of the plasma injection modulecoupled to the SBR-50 insert's wall according to an embodiment of thepresent disclosure.

FIG. 10 is a schematic view of the plasma injection module of FIG. 4 inoperation.

FIG. 11 is a schematic view of the test section for SBR-50 at theUniversity of Notre Dame (straight combustor) for testing an exampleembodiment of a plasma injection module.

FIG. 12 is a side view of the test combustor of FIG. 11 illustratingtesting of an example embodiment of a plasma injection module.

FIG. 13 is a side view of a plasma filament placed over a schlierenimage of the fuel jet.

FIG. 14 illustrates a 3D reconstruction of the plasma filament with avortical structure present from two different perspective views.

FIG. 15 a illustrates the location of the vortical structured motion ofthe plasma filament relative to a fuel concentration map.

FIG. 15 b illustrates the location of a jump structure of the plasmafilament relative to a fuel concentration map.

FIG. 16 a is a chart illustrating pressure data (pressure increaseratio) depending on fuel mass flow rate to compare the traditionalplasma ignition pattern of FIG. 3 a , traditional plasma ignitionpattern of FIG. 3 b , and for the plasma injection module of FIG. 4 inlocations proximate to the fuel injector.

FIG. 16 b is a chart illustrating pressure data (pressure increaseratio) depending on fuel mass flow rate to compare the traditionalplasma ignition pattern of FIG. 3 a (scheme #1), traditional plasmaignition pattern of FIG. 3 b (scheme #2), and for the plasma injectionmodule of FIG. 4 (scheme #3) in locations downstream the fuel injector.

DETAILED DESCRIPTION

The present disclosure is related to plasma injection modules. In someimplementations, exemplary plasma injection modules can act as a fuelinjection system and advanced ignition system simultaneously. Exemplaryconfigurations disclosed can enable combustible materials or reactivemixtures to share a common path with a plasma filament generated by ahigh voltage source. Exemplary plasma injection modules can include along plasma zone that allows plasma-reactive mixture interaction, anextended volume of initial kernel, and/or provide higher probability ofself-sustained flame holding, especially under non-optimal conditions.

In the present disclosure, plasma injection modules are disclosed thatcan improve ignition and mixing of a combustible material compared tothe case of standard transverse fuel injection illustrated in FIG. 1 ,FIG. 2 , FIG. 3 a , and FIG. 3 b . Exemplary plasma injection modulescan generate the plasma filament collocated with the fuel jet.Additionally, exemplary plasma injection modules can include permanentmagnets that produce an axial magnetic field which causes the plasmafilament to rotate about the axis of the injector. This rotation of theplasma filament increases the volumetric region exposed to the plasmafilament which increases mixing, increases the size of an ignitionkernel, and increases the volume containing highly reactive radicals.Highly reactive radicals represent chemically active species includingmolecules or atoms in electronically or vibrationally excited states.These reactive radials normally do not exist in the gas. The plasmafilaments rotation also reduces the heat loads on the materials of theplasma injection module.

I. Definitions

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. In case of conflict, the present document, includingdefinitions, will control. Preferred methods and materials are describedbelow, although methods and materials similar or equivalent to thosedescribed herein can be used in practice or testing of the presentdisclosure. The materials, methods, and examples disclosed herein areillustrative only and not intended to be limiting.

The terms “comprise(s),” “include(s),” “having,” “has,” “can,” andvariants thereof are intended to be open-ended transitional phrases,terms, or words that do not preclude the possibility of additional actsor structures. The singular forms “a,” “an” and “the” include pluralreferences unless the context clearly dictates otherwise. The presentdisclosure also contemplates other embodiments “comprising” and“consisting essentially of,” the embodiments or elements presentedherein, whether explicitly set forth or not.

II. Exemplary Plasma Injection Module

FIGS. 4-6 illustrate a plasma injection module 110 having a fuelreceiving end 114, a discharge end 118 opposite the fuel receiving end114, and an axial fluid pathway 122 extending between the fuel receivingend 114 and the discharge end 118. The plasma injection module 110 maybe used as an injection source in various locations and applications.For example, the plasma injection module 110 may be used in a supersoniccombustor (e.g., a scram jet) and may be installed on a plane wall,inside of a flameholding cavity or combustor, described in detail below,in vicinity of fuel injecting struts, etc. The plasma injection module110 is configured to receive a combustible material or reactive mixture,such as gaseous hydrocarbon fluids (e.g., ethylene, hydrogen, methane,mixtures of gaseous hydrocarbons, etc.) and other fluids such as air,oxygen, and liquid or vaporized liquid fuels like Jet A or JP-8.

The illustrated plasma injection module 110 includes an insulatorassembly 126, a voltage input connection 130 configured to receive anelectric current from high-voltage power supply source 134(schematically illustrated in FIG. 3 ), an injection tube assembly 142positioned downstream of the voltage input connection 130, and aconnection assembly 138. The connection assembly 138 extends between andcouples the insulator assembly 126 to the voltage input connection 130and to the injection tube assembly 142.

The insulator assembly 126 includes a first connection sleeve 146configured to receive the combustible or other injectable material, aninsulator 150 coupled to and downstream of the first connection sleeve146, and a second connection sleeve 154 coupled to and downstream of theinsulator 150. The first and second connection sleeves 146, 154 may beconstructed of metals capable of tolerating high temperatureapplications (e.g., steel, aluminum, etc.). The insulator 150 may beconstructed of a ceramic material (Alumina, Macor™, Shapal™, etc.) toprovide insulation between the combustible material entering thereceiving end 114 of the plasma injection module 110 and the voltagesource 134.

In the illustrated embodiment, the insulator 150 is formed to havecylindrical construction that defines a portion of axial fluid pathway122 upstream of the voltage source 134. The cylindrical construction ofthe plasma injection module 110 allows the plasma injection module 110to be inserted within combustors, such as the SBR-50 combustor 200illustrated in FIG. 7 .

In some embodiments, the use of high temperature rated connectionsleeves 146, 154 provides cost efficient connection portions for theplasma injection module 110 to be connected to a fuel line, and for theinsulator assembly 126 to be connected to the connection assembly 138upstream of the voltage input connection 130. In other embodiments, theinsulator assembly 126 may be formed by a single insulator that definesthe fuel receiving end 114 and is able to be connected to the connectionassembly 138.

In the illustrated embodiment, the connection assembly 138 is acompression fitting having a compression ring that surrounds the secondconnection sleeve 154, a compression nut 158 coupled to the secondconnection sleeve 154, a connection seat 166, and a connection tube 162coupling the compression ring to the connection seat 166. The connectionassembly 138 operably couples the insulator assembly 126 to the voltageinput connection 130 and the injection tube assembly 142. In otherembodiments, various connection assemblies may be used to couple theinsulator assembly 126 to the voltage input connection 130 and theinjection tube assembly 142.

The voltage connection input 130 includes a voltage input aperture 170that is configured to receive the voltage source 134. For example, thevoltage source 134 may be a wire that extends through the voltage inputaperture 170 and wraps around an injection tube 174 of the injectiontube assembly 142. The injection tube 174 acts as an electrode to allowthe voltage source 134 to produce a plasma filament. The voltage source134 may produce a voltage in the range of approximately 3 kilovolts (kV)to 6 kV to generate the plasma filament. Other voltages arecontemplated. In the illustrated embodiment, the voltage input aperture170 is positioned approximately transverse the axial fluid pathway 122.In other embodiments, the voltage input aperture 170 may intersect theaxial fluid pathway 122 at any angle and the voltage magnitude may bedifferent from described above.

The injection tube assembly 142 includes the injection tube 174, a firstinsulating tube 178, one or more flow inducing devices or permanentmagnets 182, a second insulating tube 184, a sleeve 186 (e.g., a metalsleeve), and a containment cap or tube 190. The injection tube 174 iscoupled to the compression ring and connection seat 166 of theconnection assembly 138. The voltage input connection 130 is coupled tothe injection tube 174 between the containment cap 190 and theconnection assembly 138 to secure the voltage input connection 130downstream of the insulator assembly 126 and upstream the injection tubeassembly 142. In the illustrated embodiment, the injection tube 174 isconstructed of a material that has a high thermal and electricconductivity (e.g., copper, brass, etc.).

The injection tube 174 can act as an electrode for the voltage source134 connected to voltage input connection 130 and forms a portion of theaxial fluid pathway 122 within the injection tube assembly 142. The fuelreceiving end 114 is constructed to electrically separate the highvoltages within the plasma injection module 110 and the metal componentsrelated to the fuel supply.

When the voltage source 134 is on, the plasma filament (228 in FIG. 10 )is formed on an outer diameter of the injection tube 174 and interactswith the combustible material to generate a highly reactive materialadjacent the discharge end 118. That is, the plasma filament is formedwithin and adjacent to the axial fluid pathway 122 and the plasmafilament may extend between the axial fluid pathway 122 and a groundedmetal wall outside of the plasma injection module 110, as 228 is shownin FIG. 10 .

The first insulating tube 178 surrounds the injection tube 174 and isformed of a non-conductive material. For example, the first insulatingtube 178 may be formed of ceramic material similar to the insulator 150.The first insulating tube 178 is sized to surround a portion of theinjection tube 174 and engage with the containment cap 190.

In the illustrated embodiment, the flow inducing device is formed as oneor more permanent magnets 182 that are constructed as cylindricalmagnets that surround the injection tube 174 and engage the firstinsulating tube 178 adjacent to the discharge end 118 of the plasmainjection module 110. The one or more permanent magnets 182 introduce anexternal magnetic field to the plasma filament, which produces a forcethat causes the plasma filament to rotate around the axis of theinjection tube 174. The rotation of the plasma filament prevents theplasma filament from maintaining a single connection point of contactbetween the voltage source and a grounded side (e.g., the combustor)which reduces the heating and evaporation of metal. The rotation alsoincreases the volume of gas exposed to the plasma filament since theplasma rotation happens on a time scale comparable or smaller than thelocal flow.

As such, the use of an external magnetic field allows the plasmainjection module 110 to influence the length and rotation of the plasmafilament to reduce heating and increase the volume of gas whichinteracts with the plasma filament. In some constructions, the magnetsmay be neodymium grade 52 permanent magnets. In other embodiments, othertypes of magnets such may be used to induce the external magnetic fieldon the filamentary plasma without adding substantial weight to theplasma injection module. In some embodiments, the axial fluid pathway122 of the plasma injection module may include a mechanical element thatprovides a tangential component to the movement of combustible fluid toproduce a swirling pattern in a flow field of the combustible fluid. Themechanical element may be used in place of the magnets 182 or inconjunction with the magnets 182.

The second insulating tube 184 is sized to surround the first insulatingtube 178 and the one or more permanent magnets 182. The secondinsulating tube 184 may be formed of a ceramic material similar to theinsulator 150 and the first insulating tube 178. The sleeve 186 is sizedto surround the second insulating tube 184. The second insulating tube184 includes a fuel discharge opening or nozzle 194 positioned adjacentthe discharge end 118 of the plasma injection module 110.

The nozzle 194 may include a geometry that enhances or suppressescertain characteristics of the flow of the plasma filament and thecombustible material during mixing and ignition of the combustiblematerial (e.g. mass flow rate, flow velocity, etc.). In the illustratedembodiment, the nozzle 194 is formed as a portion of the secondinsulation tube 184 and is tapered to form an end of the axial fluidpathway 122. In other embodiments, the nozzle 194 may be a separatecomponent of different geometry (e.g., a different profile to promote adesired flow pattern, such as a supersonic jet or swirling flow with asignificant tangential component of the gas velocity) that is secured tothe second insulating tube 184 or the sleeve 186.

The sleeve 186 is configured to couple to the containment cap 190 tosecure the first insulating tube 178, the permanent magnets 182, thesecond insulating tube 184, and metal sleeve 186 to injection tube 174relative to each other. For example, the metal sleeve 186 may have athreaded outer diameter that engages with a threaded inner diameter ofthe containment cap 190. In other embodiments, other connection methodsmay be used.

During assembly of the plasma injection module 110, the insulatorassembly 126, connection assembly 138, the voltage input connection 130,and the injection tube assembly 142 are received or provided. Theinsulator assembly 126 defines a fuel receiving end of the plasmainjection module and a first portion of the axial fluid pathway 122. Theinsulator assembly 126 is coupled to the connection assembly 138. Thevoltage input connection 130 is coupled to the injection tube 174 of theinjection tube assembly 142. The injection tube 174 is coupled to theconnection assembly 138 so the voltage input connection 130 isdownstream the insulator assembly 126. The injection tube forms a secondportion of the axial fluid pathway 122. The containment cap 190, thefirst insulating tube 178, the permanent magnet 182, the secondinsulating tube 184, the sleeve 186, and the nozzle 194 are sequentiallycoupled to the injection tube 174. More specifically, the firstinsulating tube 178 is coupled to the injection tube 174 and positionedinside the containment cap 190 to surround the injection tube 174. Theone or more permanent magnets 182 are coupled to the injection tube 174adjacent to the first insulating tube 178 and the discharge end 118 ofthe plasma injection module 110. The second insulating tube 184 iscoupled to the injection tube 174 so the second insulating tube 184surrounds and encloses the first insulating tube 178 and the one or morepermanent magnets 182. In the illustrated embodiment, the nozzle 194 isa portion of the second insulating tube 184. In other embodiments, aseparate nozzle may be coupled to the assembly. It should be appreciatedthat coupling the nozzle 194 to the plasma assembly may incorporateeither construction. The sleeve 186 is coupled to the injection tube 174so the sleeve 186 surrounds the second insulating tube 184. The metalsleeve 186 configured to be securable to the containment cap 190 tosecure the first insulating tube 178, the permanent magnets 182, and thesecond insulating sleeve 184 to define the injection tube assembly 142downstream of the voltage connection input 130.

III. Exemplary Combustor for Plasma Injection Modules

With reference to FIGS. 7-9 , a non-limiting application of the plasmainjection module is illustrated. The plasma injection module 110 iscoupled to an experimental combustor 200 using an insert for SBR-50 atthe University of Notre Dame having a flowside wall 208 without flameholding cavity, side walls 212, an opposing wall 204 opposite theflowside wall 208, and pressure taps 216 positioned on the flowside wall208. A plurality of plasma injection modules 110 are inserted within aplurality of fuel ports on the SBR-50 insert 200 such that the fuelreceiving end 114 of the plasma injection module 110 extends from theopposing wall 204 of the combustor 200 and the nozzle 194 and thedischarge end 118 of the plasma injection module is flush with theflowside wall 208. In some embodiments, the nozzle 194 of the plasmainjection module 110 may be inserted within a ceramic insert 220 thathas an obligated cross section (FIG. 8 ). The ceramic insert 220 allowsfor the plasma filament to travel a distance along the ceramic insert220 before the plasma filament interacts with the top wall 208 to form aground.

FIG. 9 illustrates a schematic of the plasma injection module 110operably coupled to the SBR-50 combustor 200. During operation of theplasma injection module 110, the first connection sleeve 146 (FIG. 5 )is coupled to a fuel line 224 that receives a combustible material. Thecombustible material moves through the axial fluid pathway 122 of theplasma injection module 110. The high voltage source 134 introduces aplasma filament 228 to the axial fluid pathway 122 via the voltageconnection input 130.

Once the plasma filament 228 (FIG. 10 ) and the combustible fuel entersthe injection tube assembly 142, the one or more permanent magnets 182(FIG. 5 ) introduce an external magnetic field which produces a force onthe plasma filament 228 to cause the plasma filament 228 to rotate. Therotation increases the volume of combustible material exposed to theplasma filament 228 since the plasma rotation happens on a time scalecomparable or smaller than the local flow. As a result, the plasmafilament 228 and combustible material begins mixing to generate a highlyreactive material adjacent the discharge end 118 of the plasma injectionmodule 110. The generation of the highly reactive material increases theefficiency of ignition and combustion before the plasma filament 228 andthe combustible material are introduced to a supersonic crossflow 232with oxidizer.

As illustrated in FIG. 10 , the plasma filament 228 enters the axialfluid pathway 122 adjacent the discharge end 118 and is generating thehighly reactive material. The highly reactive material interacts withthe supersonic flow 232 and forms a recirculation zone for ignitionalong the flowside wall 208. For example, the plasma filament may coupleto a local flow region during transverse injection into the supersonicflow 232 to elongate the length of the plasma filament 228 in adownstream direction from the discharge end 118. In some embodiments,the length of the plasma 228 may elongation to a distance greater than100 millimeters from the discharge end 118. Once the plasma filament 228reaches an end portion of the ceramic insert 220, the plasma filament228 grounds on the top wall 208 of the combustor 200. The plasmafilament 228 formed by the plasma injection module 110 locates withinthe mixing layer of the injection tube 174 which increases the abilityto ignite and combust the highly reactive material.

IV. Methods of Use

Exemplary plasma injection modules may be used within a flameholdingcavity, on a plane wall, behind mixing components, or the like. Anexemplary operation of plasma injection module 110 operating withinapparatus as shown in FIGS. 7-9 is discussed below.

During an exemplary operation of the plasma injection module 110, thefirst connection sleeve 146 is coupled to a fuel line that receives acombustible material. The combustible material moves through the axialfluid pathway 122 of the plasma injection module 110. The high voltagesource 134 introduces a plasma filament to the axial fluid pathway 122via the voltage connection input 130. The combination of the plasmainjection module 110 and the combustor forms an ignition system thatincreases an area of ignition between the combustible fuel and theplasma filament.

Once the plasma filament and the combustible fuel enters the injectiontube assembly 142, the one or more permanent magnets 182 (FIG. 5 )generates an external magnetic field and produces a force on the plasmafilament to cause the plasma filament to rotate. In other embodiments,an alternative flow inducing device may cause the plasma filament torotate. The rotation increases the volume of combustible materialexposed to the plasma filament because the plasma rotation happens on atime scale comparable or smaller than the local flow. As a result, theplasma filament 228 and combustible material begin mixing to generate ahighly reactive material adjacent the discharge end 118 of the plasmainjection module 110. The generation of the highly reactive materialdecreases the ignition time and increases the efficiency combustion.

IV. Experimental Examples

The construction and methods of the disclosure may be better understoodby reference to the following examples, which are intended as anillustration of and not a limitation upon the scope of the disclosure.

The experiments were performed in the supersonic blow-down wind tunnelSBR-50 at the University of Notre Dame. The combustor cross section atthe exit of the converging-diverging nozzle was 76.2 mm in width (Y) and76.2 mm in height (Z), with a 1° expansion half-angle and a total length(X) of 610 mm measured to the diffuser, as shown in FIG. 11 . The fuelinjectors and electrical discharge generators were flush-mounted on aplane wall as a single unit, indicated in FIG. 11 as“PIM”—Plasma-Injection Module. The test section of the SBR-50 high-speedcombustion facility were equipped with two pairs of quartz windowsplaced as the side walls of the duct for optical access (FIG. 12 ).Ohmic heating was used to heat the air in the plenum chamber up toT0=750 K, providing a non-vitiated oxidizer for the combustion chamber.

In the experimental examples, the combustion chamber was set to have thefollowing conditions: initial Mach number (airflow) M=2; total pressureP0=1-2.2 bar; stagnation temperature T0=300-750 K, air mass flow rate{dot over (m)}_(air)=0.5-2 kg/s; duration of steady-state aerodynamicoperation t=1-2 s. Instrumentation available for this test includes:wall pressure taps; fast camera imaging Photron FastCam (b/w) and CasioEX-FH100 Camera (color); high-definition schlieren system; opticalemission spectroscopy (OES) based on OceanOptics™ spectrometers, and aset of electrical probes.

EXAMPLE 1: PLASMA MORPHOLOGY

The experiment was conducted to evaluate the possible role of plasmamorphology on ignition of combustible material. In the experiment, thecombustible material was ethylene and is in a range of fuel-to-totalmolecular number density ratio N_(C2H4)/N=0.25-0.5, which corresponds toa rich mixture with equivalence ratio (ER) of 5-15. The ethylene isprovided through a plasma injection module to form a fuel jet ofethylene.

Three-dimensional reconstructions of plasma filaments revealed that thethree major types of movement that the plasma filaments follow arevortex-induced rotation, fast side-to-side transition (“jump”), andcurling back upstream in the vicinity of the filament connection to thegrounded wall. The first coherent structure that was observed is avortical behavior which manifests as a spiral shape of the plasmafilament, as shown in FIGS. 14 and 15 a.

When the plasma filament enters the highly turbulent portion of the fueljet, the plasma filament shape and dynamics are governed by flow fieldrather than the configuration of the self-sustained electric fieldbecause ion drift is an order of magnitude slower than local convectionmovement of flow. Periodic oscillations (rotation) of the plasmafilaments are observed, which is an essential feature of the plasmafilaments' behavior. The effectiveness of plasma impact on the ignitionand mixing can significantly varied depending on the filamentary plasmaposition in the flowfield.

FIGS. 15 a and 15 b illustrate the location of the plasma filamentstructure compared to the average fuel concentration in the fuel-airmixture. The location indicated as x/d=5 corresponds to distance x=15-35mm from the fuel port. In this position, the plasma filamentdemonstrates the vortically structured motion. As seen in FIG. 15 a ,the vortical portion of the filament is located inside of the fuel jetand rotates near the relative concentration of ethylene. The secondfilament structure (“jump”) is situated nearby the cross-section x/d=25which corresponds to x=65-87 mm distance from the injection port in thecurrent study. FIG. 15 b shows the position of the “jump” pattern inrelation to the ethylene fuel distribution inside of the fuel jet.Contrary to the vortical pattern shown in FIG. 16 a , the “jump” patternis located nearby/inside of the region with stoichiometric fuel-to-airratio shown with the white line in the figure.

As a result, a conclusion drawn for the experiment is that the plasmafilament is rarely located in the regions of maximum fuel concentrationand never leaves the fuel jet into the freestream flow. The fuel-airmixing and the plasma filament/ignition source develop simultaneously.Due to intensive plasma-chemical kinetic processes, the ignition zone inthe described plasma injection module 110, described with reference toFIG. 4-6 , is located in the optimal position within the mixing layerfor flame initiation.

This phenomenon, along with the much larger volume and energydeposition, can be utilized to widen the operational limits of ascramjet engine by providing enhanced ignition/re-ignition times,reducing the overall length of the combustor, and perhaps a highercombustion efficiency due to the enhanced mixing. The use of permanentmagnets, as illustrated in the plasma injection module described withreference to FIGS. 4-6 , add a significant rotating momentum to theplasma filament which leads to additional mixing intensification.Additionally, the external magnetic field is also beneficial to controlthe plasma filament of a plasma injection module, to reduce heating, andincrease the volume of gas which interacts with the plasma filament.

EXAMPLE 2: PRESSURE DISTRIBUTION

The experiment was conducted to evaluate combustion and ignition whilevarying parameters such as flow pressure, the plasma power (i.e., fromthe voltage source), and fuel injection rates.

For this test series three modules (PIMs) were installed in thecombustor (FIGS. 7-11 ). Electrical power was turned on for a durationof 0.1 to 0.2s starting at nearly the same time as the beginning of thefuel injection and fuel injection continues for a short period of timeafter the end of the discharge. Ethylene was used as the fuel in thistest series: the fuel mass flowrate was up to {dot over (m)}_(C2H4)=8.5g/s distributed through three plasma injection modules with a fuelnozzle diameter d_(f)=3.1 mm providing a subsonic/sonic jet with ajet-to-freestream momentum flux ratio (J) in the range 0.1 to 1 and anoverall equivalence ratio (ER) in the range of 0 to 0.2.

With strong combustion, a zone of bright luminescence concentrates closeto the plasma injection modules (FIG. 12 ), whereas with weak combustionand partial oxidation there appears a long tail of luminosity in a zonefar from the plasma injection modules. For realization of strongcombustion mode, the plasma power was sufficiently high, in a range ofW_(pl)=10-20 kW for M=2, P₀=1.7 bar, T₀=300 K, and {dot over(m)}_(C2H4)=2-8 g/s. Increasing the pressure, fuel mass flow rate, orflow velocity requires higher plasma power. For hydrogen combustion thepower threshold is significantly lower.

The scheme of plasma assistance with the plasma-injection modules 110,as described in FIGS. 3-5 , demonstrates significant benefits comparedto the previously tested configurations with the electric dischargelocated both upstream (FIG. 3 a ) and downstream (FIG. 3 b ) of the fueloutlet. Specifically, it was determined that ignition and flameholdingare observed over a wider range of flow parameters and fuel injectionrates.

FIGS. 16 a and 16 b illustrate a comparison of pressure data dependingon fuel mass flow rate, obtained for the configuration with dischargegeneration upstream of the fuel injector (scheme #1—FIG. 3 a ),downstream of the fuel injector (scheme #2—FIG. 3 b ), and for theplasma injection module 100 (scheme #3—FIG. 4 ). The flow parameters(M=2, P_(st)=0.2-0.27 Bar) and discharge power (W_(pl)=12-18 kW) aresimilar in all cases, axial location X is measured from the fuelinjection cross-section (i.e., the center of the discharge end 118 ofthe plasma injection module 100). FIG. 16 a illustrates the pressuredata in locations of measuring points in proximity of fuel injector,(i.e., a distance from x=40-50 mm). FIG. 16 b illustrates the pressuredata in locations in downstream zones (i.e., a distance from x=175-190mm).

FIG. 16 a and FIG. 16 b demonstrates a remarkable difference between theperformance of three schemes applied for plasma-based ignition andflameholding under conditions of low gas temperature, non-premixedcomposition, and low overall equivalence ratio, ER<<1. The scheme #1exhibits more effective ignition at low fuel flow rates, {dot over(m)}C₂H₄<2 g/s. The last configuration scheme #3, however, shows muchbetter performance at higher values of the fuel injection, {dot over(m)}C₂H₄>2 g/s, where the scheme #1 is limited to partial oxidation withfairly insignificant increase of pressure. To interpret this difference,two key moments need to be pointed out: (1) in scheme #1, the dischargewas sustained in air, while in scheme #3 the discharge is sustained inthe fuel (inside the axial fluid pathway 122 of the plasma injectionmodule 100) as well as in the fuel-air mixture; and (2) the flowstructure in the present configuration #3 is significantly differentcomparing to scheme #1.

Specifically, the near-surface quasi-DC electric discharge used inscheme #1 produces a “closed” flow separation zone (a separation bubble)downstream of the discharge, with high concentrations of chemicallyactive species, such as atomic oxygen (O) andelectronically/vibrationally excited nitrogen (N₂*). The fuel, afterbeing injected into this zone, has sufficiently long residence time tomix with plasma-activated air and ignite.

After ignition, the volume of this zone increases and forms an extendedsubsonic flow zone without obvious reattachment downstream. At furtherincrease of fuel injection a local concentration of the fuel inseparation zone exceeds the rich limit of ignition. In contrast to thispattern, in the scheme #3 the discharge is localized along the fuelinjection jet, which generates reactive species and radicals, such as H,CH, C₂H₃, etc., by electron impact, and enhances mixing by convectingthe unstable plasma filament with the injection jet. Based on thepresent results, it appears that plasma filament convection with theflow becomes significant only at sufficiently high fuel injection speed,comparable with the main airflow velocity.

It should be understood that the disclosure is not limited in itsapplication to the details of construction and the arrangement ofcomponents in the instant disclosure or corresponding drawings. Thedisclosure is capable of other embodiments and of being practiced or ofbeing carried out in various ways.

What is claimed is:
 1. A plasma injection module comprising: a fuelreceiving end configured to receive a combustible material; a dischargeend opposite the fuel receiving end; an axial fluid pathway extendingbetween the fuel receiving end and the discharge end; an insulatorassembly defining a first portion of the axial fluid pathway proximateto the fuel receiving end; an injection tube assembly positioneddownstream of the insulator assembly, the injection tube assemblycoupled to the insulator assembly, the injection tube assemblyincluding: an injection tube defining a second portion of the axialfluid pathway adjacent to the discharge end, the injection tube formedof an electrically conductive material; and a nozzle surrounding theinjection tube, the nozzle defining a fuel discharge opening proximatethe discharge end; a voltage input connection arranged between theinsulator assembly and the injection tube assembly, the voltage inputconnection being configured to secure a voltage source to the injectiontube to form a plasma filament within and adjacent to the axial fluidpathway; and a flow inducing device coupled to the injection tubeproximate to the discharge end.
 2. The plasma injection module of claim1, wherein the flow inducing device is a permanent magnet arrangedannularly about the injection tube.
 3. The plasma injection module ofclaim 2, wherein the injection tube assembly further comprises: a firstinsulating tube surrounding the injection tube; a second insulating tubesurrounding the first insulating tube and the permanent magnet; and acontainment cap or tube surrounding the injection tube, the first andsecond insulating tubes, the permanent magnet, and the nozzle to secureeach component relative to each other.
 4. The plasma injection module ofclaim 3, wherein the nozzle is formed as a portion of the secondinsulating tube adjacent the discharge end of the plasma injectionmodule.
 5. The plasma injection module of claim 1, wherein the flowinducing device is a mechanical element that provides a tangentialcomponent to the movement of the combustible material to produce aswirling pattern of a flow field of the combustible material.
 6. Theplasma injection module of claim 1, wherein the plasma injection moduleis configured to be coupled to a combustor having one or more fuel portspositioned on a flowside wall, wherein the nozzle of the plasmainjection module is flush-mounted with the flowside wall of thecombustor.
 7. The plasma injection module of claim 6, wherein the flowinducing device, during operation, interacts with the plasma filament tocause rotation of the plasma filament and increase an area of ignitionbetween the plasma filament and the combustible material to generate thehighly reactive material at the discharge end.
 8. The plasma injectionmodule of claim 1, further comprising a connection assembly positionedbetween the insulator assembly and the injection tube assembly, andwherein the connection assembly defines a third portion of the axialfluid pathway.
 9. The plasma injection module of claim 8, wherein theconnection assembly further comprises a compression ring, a compressionseat, and a connection tube coupling the compression ring to thecompression seat.
 10. The plasma injection module of claim 1, whereinthe insulator assembly further comprises: a first connection sleeveconfigured to receive the combustible material; an insulator coupled toand downstream the first connection sleeve; and a second connectionsleeve coupled to and downstream the insulator.
 11. A plasma injectionmodule, comprising: a fuel receiving end configured to receive acombustible material; a discharge end opposite the fuel receiving end;an axial fluid pathway extending between the fuel receiving end and thedischarge end, an insulator assembly defining a first portion of theaxial fluid pathway proximate to the fuel receiving end; a connectionassembly positioned downstream of the insulator assembly and defines asecond portion of the axial fluid pathway, an injection tube assemblypositioned downstream of the insulator and connection assembly, theinjection tube assembly coupled to the insulator assembly via theconnection assembly, the injection tube assembly including: an injectiontube defining a third portion of the axial fluid pathway adjacent to thedischarge end, the injection tube formed of an electrically conductivematerial; a permanent magnet arranged annularly about the injection tubeproximate to the discharge end; and a nozzle surrounding the injectiontube and the permanent magnet, the nozzle defining a fuel dischargeopening proximate the discharge end; and a voltage input connectionarranged downstream of the insulator assembly and the connectionassembly and upstream of the injection tube assembly, the voltage inputconnection being configured to secure a voltage source to the injectiontube to form a plasma filament within and adjacent to the axial fluidpathway.
 12. The plasma injection module of claim 11, wherein theconnection assembly further comprises a compression ring, a compressionseat, and a connection tube coupling the compression ring to thecompression seat; and wherein during operation the permanent magnetproduces a magnetic field that interacts with the plasma filament torotate the plasma filament and increase an area of ignition between theplasma filament and the combustible material at the discharge end. 13.The plasma injection module of claim 12, wherein the insulator assemblyfurther comprises: a first connection sleeve configured to receive thecombustible material; an insulator coupled to and downstream the firstconnection sleeve; and a second connection sleeve coupled to anddownstream the insulator.
 14. The plasma injection module of claim 13,wherein the injection tube assembly further comprises: a firstinsulating tube surrounding the injection tube; a second insulating tubesurrounding the first insulating tube and the permanent magnet; and acontainment cap or tube surrounding the injection tube, the first andsecond insulating tubes, the permanent magnet, and the nozzle to secureeach component relative to each other.
 15. The plasma injection moduleof claim 14, wherein the nozzle is formed as a portion of the secondinsulating tube adjacent the discharge end of the plasma injectionmodule.
 16. The plasma injection module of claim 11, further comprisinga mechanical element that provides a tangential component to themovement of the combustible material to produce a swirling pattern of aflow field of the combustible material, wherein the mechanical elementis used in place of the permanent magnet.
 17. An ignition systemcomprising: a combustor having one or more fuel ports positioned on aflowside wall, and a plasma injection module coupled to the combustor,the plasma injection module comprising: a fuel receiving end configuredto receive a combustible material; a discharge end opposite the fuelreceiving end, the discharge end being positioned proximate the flowsidewall; an axial fluid pathway extending between the fuel receiving endand the discharge end; an insulator assembly defining a first portion ofthe axial fluid pathway proximate to the fuel receiving end; aninjection tube assembly positioned downstream of the insulator assembly,the injection tube assembly coupled to the insulator assembly, theinjection tube assembly including: an injection tube defining a secondportion of the axial fluid pathway adjacent to the discharge end, theinjection tube formed of an electrically conductive material; and anozzle surrounding the injection tube, the nozzle defining a fueldischarge opening proximate the discharge end; a voltage inputconnection arranged between the insulator assembly and the injectiontube assembly; and a flow inducing device coupled to the injection tubeproximate to the discharge end.
 18. The ignition system of claim 17,wherein the nozzle of the plasma injection module is flush-mounted withthe flowside wall of the combustor, wherein rotation of the plasmafilament to prevents the plasma filament from maintaining a singleconnection point between the voltage source and the flowside wall of thecombustor.
 19. The ignition system of claim 17, wherein the flowinducing device is a permanent magnet arranged annularly about theinjection tube.
 20. The ignition system of claim 17, wherein the plasmainjection module further comprises a connection assembly positionedbetween the insulator assembly and the injection tube assembly, andwherein the connection assembly defines a third portion of the axialfluid pathway; wherein the flow inducing device, during operation,interacts with the plasma filament to rotate the plasma filament andincrease an area of ignition between the plasma filament and thecombustible material to generate the highly reactive material at thedischarge end; and the voltage input connection being configured tosecure a voltage source to the injection tube to form a plasma filamentwithin and adjacent to the axial fluid pathway.